The inland waterway system of the United States is an important transportation resource. In 2004 over 625 million tons of cargo was moved over it using 1% of the total fuel consumption for freight transport of 16% of the nation's freight. (The U.S. Waterway System—Transportation Facts, U.S. Army Corps of Engineers, 2005). (National Transportation Statistics, Bureau of Transportation Statistics (BTS), Tables 4-5 and 5-7, 2006). Further, inland maritime transportation relies on passage through 212 locks. (U.S. Army Corps of Engineers, 2005).
“Outdrafts,” artificially induced currents directed away from a dam, are created by the actuation of dams. Tow pilots approaching navigation locks around a dam compensate for the outdraft to avoid hitting lock walls.
Not compensating for outdrafts may result in accidents that cause injury or loss of life and property as well as damage to embankments. (Waterways Action Plan, Joint Project of the Marine Industry, U.S. Coast Guard and U.S. Army Corps of Engineers, 2006). For example, the Elizabeth M. was exiting the Montgomery Locks northbound on the Ohio River on Jan. 9, 2005. The lead two barges in tow broke loose after being caught in an outdraft estimated at 13-15 mph. When the pilot tried to correct, the tow and barges were swept into the dam, killing four crew members. (News Summary for January 17-23, 2005, The Waterways Journal, 2005).
Other accidents have resulted in barges obstructing inland maritime traffic. The M/V James Buky blocked the lock at the Cannelton Dam in January 1991 and the M/V Captain Bill blocked the lock at the Smithland Dam in April 2005. In each case, barges broke free as a result of improper compensation for the outdraft. In all cases, knowledge of the outdraft will insure efficient approaches, providing tow pilots with the necessary time to compensate for outdraft.
Refer to FIG. 1 showing the prior art, i.e., lack of a formal outdraft notification system. In practice, a vessel (not shown separately) navigating downstream in the direction of the arrow 107 approaches a lock chamber 106 at a dam 104 through a channel 103 bordered by walls 101, 102 that act to align the vessel with the lock chamber 106. Guard walls 102, located in the upper (upstream) lock approach, protect vessels against an induced current (not shown separately) created by discharges downstream from the dam 104. Guide walls 101 “guide” vessels into the channel 103 on the downstream passage and align vessels with lock entry through gates 105 on the upstream passage.
Refer to FIG. 2 showing the prior art (from an overhead perspective), i.e., lack of a formal outdraft notification system. There may be an increased hazard to navigation created by outdraft 201 of unknown amplitude and direction at the Guard wall 102. This “unknown” (i.e., unmeasured and un-reported) outdraft 201 makes it more difficult to maneuver a tow being “pushed” downstream by the river.
A towboat traveling on a downriver course (arrow 107) reduces speed to less than one knot in order to safely align with the lock chamber 106 and avoid impact with the Guard wall 102. In an upper lock approach, water flows across the lock and towards the dam 104, forming a cross current 201 for which a pilot must compensate. Typically, this current is generated by a gated spillway section of the dam 104 that controls discharges downstream. This cross current 201, commonly called outdraft current or simply outdraft 201, directs the bow of the tow or barge toward the spillway of the dam 104, altering the effects of the “normal” downstream current that is known to the pilot.
Presently, estimating velocity and direction of outdrafts is accomplished by fixed objects such as buoys. Navigating through outdraft by feel alone is not sufficient to reduce risk, however. Moreover, existing communication methods, such as large signs displaying “outdraft present” as well as informal discussions between passing tow pilots, do not quantify the direction and speed of the outdraft.
Velocity of a current, including those generated as outdraft 201, may be measured using Acoustic Doppler Current Profiling (ADCP). ADCP employs the Doppler Effect, transmitting short pulses of electromagnetic energy at acoustic wavelengths and receiving echoes thereof. Echoes return from particulates such as silt, sediment, biological matter and bubbles suspended in the water. (Acoustic Doppler Current Profiler: Principles of Operation: A Practical Primer, R.D. Instruments, 1996). Estimates of a current's velocity and direction are obtained by processing of the Doppler data.
The Physical Oceanographic Real-Time System (PORTS®), developed in 1989 and used in Tampa Bay, disseminates information on safe navigation, oil spills, search and rescue, fishing and existing weather conditions. (Appell, Gerald F., The Development of Real Time Port Information System, IEE Journal of Oceanic Engineering, Vol. 19, No. 2, 1994, pp. 149-157). The PORTS® system employs two measurement stations using ADCPs, other meteorological sensors, and a data acquisition and information dissemination system (DAS/IDS). The ADCPs are located on the bay floor to monitor currents from near the bottom to near the surface and transmit pulses at pre-programmed intervals so that a six-minute reading averages about 345 pulses.
In the Houston Ship Channel, another application of PORTS employs an ADCP system to monitor currents in real time. (Appell, Gerald F. Design and Tests of Real Time Sontek ADP System, IEE Journal of Oceanic Engineering, pp. 289-292, 1996). The system uses a profiler specifically designed for shallow water. It is polled on request by a remote station through a serial cable linked to land and data on the current is recorded internally. PORTS® information for the channel is available as recorded voice, online, or both.
A system like PORTS® is used to collect data for hydrodynamic and water quality modeling in New York Harbor. (Coomes, C. A., Real Time ADCP Current Measurement System for the New York Harbor Area, OCEANS '95, Conference Proceedings., Vol. 2, pp. 1381-1385, 1995). Data are stored internally and communicated via serial link to a computer in real time.
HADCP is used in a current profiling project in Lillebaelt, Denmark for an inexpensive method of determining flow in narrow navigation passages. A traditional ADCP and a HADCP are used, a two beam ADCP unit validating data from the HADCP device. (Rorbaek, K., Horizontal Current Profiling in Lillebaelt Denmark, DHI Water & Environment, 2001).
One approach to alerting a tow pilot to currents around a lock is verbal communication from the lock master. For example, viewing data from an ADCP sensor, the lock master relays information to a tow pilot via VHF radio. Because vessels and the lock are required to communicate during locking, this was considered a viable means of guiding the tow. Data could be transmitted over systems such as wireless Local Area Networks (LAN), radios, and Automatic Identification Systems (AIS). This verbal communication is not “automated” and may occur too late in some situations to be of help to the tow pilot.
Automatic Identification Systems (AIS) comprise radio transponders required by the International Maritime Organization (IMO) for use in certain operating areas. Integrating VHF and GPS technology, AIS provides information concerning vessel Maritime Mobile Service Identity (MMSI) numbers, course, speed, ports of call and the like. (What is the Automatic Identification System (AIS)?, U.S. Coast Guard, 2006). Through AIS communication, mariners gain a valuable method by which vessels may exchange data in real time. For example, when overlaid on an electronic chart, ships within 30-50 miles of an AIS-equipped vessel are indicated as a velocity vector.
Provision of the information is automated and made available to a towboat pilot in real time on an electronic chart display as vectors, similar to warnings of vessels in the area. Within the AIS standards, a message format contains both meteorological and hydrologic data, termed “met/hydro” messages. Table 1 lists information that may be contained in these messages. (International Association of Marine Aids to Navigation Lighthouse Authorities (IALA), IALA Guideline No. 1028 on The Automatic Identification (AIS) Volume 1, Part I Operational Issues, Edition 1.3, December 2004).
ADCP units are available from several commercial sources. Initially, ADCP units profiled currents vertically from a riverbed or ocean floor. Recently developed ADCP equipment, the Horizontal ADCP (HADCP) is a side-looking device able to measure the velocity and direction of a horizontal current. HADCPs have been used in such diverse applications as deep draft shipping channels and estuaries, oil exploration, and in support of production rigs and power plants. (Work Horse Horizontal ADCP Operation Manual, R.D. Instruments, 2004). Neither ADCP nor HADCP has been used to help tow pilots during lock and dam transition until an embodiment of the present invention was tested for that purpose.
TABLE 1Content of Meteorological and Hydrological Messages.ParameterNo. of bitsDescriptionMessage ID6Identifier for Message 8; always 8Repeat Indicator2Used by the repeater to indicate how many times a msg has beenrepeated.Source ID30MMSI number of source stationSpare2Not used. Should be set to zero.IAI16DAC = 00l; FI = 11Latitude24Measuring position, 0 to +/− 90 degrees, 1/1000th minuteLongitude25Measuring position, 0 to +/− 180 degrees, 1/1000th minuteDate and time16Time of transmission, Day, hour, minute, (ddhhmm in UTC)Average wind speed7Average of wind speed values for the last 10 minutes. 0-120 kts, 1 ktWind gust7Wind gust is the maximum wind speed value reading during the last10 minutes, 0-120 kts, 1 ktWind direction90-359 degrees, 1 degreeWind gust direction90-359 degrees, 1 degreeAir temperature11Dry bulb temperature −60.0 to +60.0 degrees Celsius 0.1 of a degreeRelative humidity70-100%, 1%Dew point10−20.0-+50.0 degrees, 0.1 degreeAir pressure9800-1200 hPa, 1 hPaAir pressure tendency20 = steady, 1 = decreasing, 2 = increasingHorizontal visibility80.0-25.0 NM, 0.1 NMWater level (incl. tide)9Deviation from local chart datum,. −10.0 to +30.0 m 0.1 mWater level trend20 = steady, 1 = decreasing, 2 = increasingSurface current speed (incl.80.0-25.0 kts 0.1 kttide)Surface current direction90-359 degrees, 1 degreeCurrent speed, #28Current measured at a chosen level below the sea surface, 0.0- 25. kts, 0.1 ktCurrent direction, #290-359 degrees, 1 degreeCurrent measuring level, #25Measuring level in m below sea surface,. 0-30 m 1 mCurrent speed, #380.0-25.0 knots, 0.1 knotCurrent direction, #390-359 degrees, 1 degreeCurrent measuring level, #35Measuring level in m below sea surface,. 0-30 m 1 mSignificant wave height80.0-25.0 m, 0.1 mWave period6Period in seconds, 0-60 s, 1 sWave direction90-359 degrees, 1 degreeSwell height80.0-25.0 m, 0.1 mSwell period6Period in seconds, 0-60 s, 1 sSwell direction90-359 degrees, 1 degreeSea state4According to Beaufort scale (manual input?), 0 to 12, 1Water temperature10−10.0-+50.0 degrees, 0.1 degreePrecipitation (type)3According to WMOSalinity90.0-50.0%, 0.1%Ice2Yes/NoSpare6Total Number of bits352Occupies 2 slots
A tow pilot uses successive fixes relative to surrounding geographic points, area hydrology and current meteorology. (Hayler, W. B., American Merchant Seaman's Manual, 7th edition, 2003). Using nautical charts, the pilot also employs dead reckoning based on present course, distance and speed. The pilot combines successive fixes and dead reckoning plots to adjust course and speed in accordance with external factors such as current, wind, waterway conditions, hazards and the like. Modern towboats have a functional display, typically referred to as an integrated navigation system (INS) or integrated bridge system (IBS), displaying a variety of these navigational resources on a single interface. (Olsen, Oddmund, Electronic Navigation Systems, Leknes, Norway: Poseidon, 2002).
Through interface with AIS, radio communications, or other wireless technology, vectors representing current direction and velocity may be projected onto the charts of the INS or IBS to alert tow pilots. For example, communicating the direction and velocity of real-time current data around a lock provides required information for minimizing risk in navigating a lock.
Risks due to outdrafts at dams can be reduced or eliminated by employing a system and method for measuring and communicating outdraft direction and velocity in real time. Preferably the system incorporates commercial-off-the-shelf (COTS) hardware. A system and method for measuring and communicating outdraft velocity and direction was tested on the Tennessee-Tombigbee Waterway at the Tom Bevill Lock and Dam, known to have a strong outdraft upstream of the lock. Testing demonstrated the viability of a system and method for measuring and reporting outdraft measurements at locks as well as potential for its use at bridges and in harbors.